She is the poshest woman in Spain, a grandee with such extensive estates that she can reputedly cross the country without once leaving the lands accumulated by her aristocratic family over five centuries.

Now the flamboyant Duchess of Alba has, at 82, found herself at the centre of a row involving a younger lover, wedding plans, her disapproving children and claims that she may be losing her mind.

Her six children have publicly denied asking a court to declare the love-struck octogenarian mentally incompetent in order to prevent her marrying a suave antique collector called Alfonso Díez - who is 24 years her junior.

"They have not initiated court proceedings to have their mother the Duchess of Alba, whom they respect profoundly, declared incompetent," a statement issued in the children's names said.

News that María del Rosario Cayetana Alfonsa Victoria Eugenia Francisca Fitz-James Stuart y de Silva - as the duchess is also known - had been hatching a secret plan to marry Díez sent Spain's gossip industry into a frenzy of speculation last month.

Reports soon circulated of a family bust-up as the duchess herself held forth about her children's hypocrisy, and leaked medical documents suggested she may not be entirely in control of her actions.

"It is true that we thought of marrying," she told Hola! Magazine last month. "The difficult thing was that my children did not understand ... I must admit that I got very angry," said the duchess, pointing out that her children - five of whom are divorced - changed partners far more frequently than she had ever done. A press statement from the House of Alba later denied that a wedding was planned.

The duchess has long been a staple of Spain's gossip industry and has frequently been pictured with bullfighters and flamenco dancers. Her second husband, whom she married after her children's father died, left her a widow seven years ago. She has suffered serious health problems. El País newspaper reported that it had seen medical reports showing that the duchess may have dementia.

Her death could lead to fighting over one of Spain's wealthiest and most culturally important legacies. The owner of many palaces, she also has an art collection replete with works by Goya, Velázquez and Rembrandt. One of her best-known pictures is a Goya portrait of a previous Duchess of Alba who was said to be the painter's lover.